It is a huge mistake that you think Vietnam leadership is pro-China. On the surface, Vietnam government is neutral but on the media it is the opposite. They are even more biased than the western media. And media in Vietnam is very tightly controlled by the gov. It is the government that make the public very anti-China in the first place. Begin with Le Duan, tamed down in the 2000s and surge from 2010s when Vietnam turned more nationalistic.India will never be a friend of China. Zhou Enlai tried to end the border conflict already back in the 1950s by proposing mutual acceptance of border areas. China would get Aksai Chin and India would get what they call Arunachal Pradesh. India rejected it then and has rejected it since.
Don't fool yourself. India is only moving towards China because circumstances forced them to. There is great distrust among Indians, particularly the Hindutva types. Ironically, it's precisely these self-styled nationalists who were the biggest boosters of a US-India partnership. The left-secular Congress had traditionally favoured a more balanced foreign policy, closer to Russia and the global south.
For the Philippines, public sentiment is overwhelmingly anti-China. For Vietnam, it's more complex. The leadership is pretty pro-China but the people beneath the elites are more pro-US. This is weird, given the brutal Vietnam war. China's brief border skirmish was a nothingburder in comparison.
I think the main reason for all of this is the diaspora. Indian, Vietnamese and Filipinos diasporas are all very numerous in the West and this creates a natural cultural link to elites back home. China is a much more closed society, so there hasn't been the opportunity to create foreign diasporas. In addition, China was simply too poor to be attractive for immigrants until recently. For these reasons, people-to-people ties are scarce compared to what the West can offer these countries. China also has its own enclosed cultural space. India consumes lots of Western culture, whereas China largely does not except a few films on the margins.
Making a rational argument on economics is a very Chinese way of thinking, because Chinese people are pragmatic and rational. But people in global south countries often have emotional and social factors swaying their decisions. It's the same reason why elites in countries like Iran or Armenia keep running into the arms of the West even if it doesn't make much sense from a cold geopolitical standpoint. Because it's an emotional decision.